diff --git a/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm b/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm
index f2a5711b7..eec2c5512 100644
--- a/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm	
+++ b/OSBindings/Mac/Clock SignalTests/x86DecoderTests.mm	
@@ -142,7 +142,7 @@ namespace {
 		0x23, 0xaa, 0x2c, 0x5b, 0x2a, 0xd2, 0xf7, 0x5f, 0x18, 0x86, 0x90, 0x25, 0x64, 0xb7, 0xc3
 	}];
 
-	// 68 instructions are expected.
+	// 63 instructions are expected.
 	XCTAssertEqual(instructions.size(), 63);
 
 	// sub    $0xea77,%ax
@@ -301,4 +301,19 @@ namespace {
 	[self assert:instructions[62] operation:Operation::MOV size:1 operand:0xc3 destination:Source::BH];
 }
 
+- (void)test83 {
+	[self decode:{
+		0x83, 0x10, 0x80,	// adcw   $0xff80,(%bx,%si)
+		0x83, 0x3b, 0x04,	// cmpw   $0x4,(%bp,%di)
+		0x83, 0x2f, 0x09,	// subw   $0x9,(%bx)
+	}];
+
+	// 68 instructions are expected.
+	XCTAssertEqual(instructions.size(), 3);
+
+	[self assert:instructions[0] operation:Operation::ADC size:2 source:Source::Immediate destination:Source::IndBXPlusSI operand:0xff80];
+	[self assert:instructions[1] operation:Operation::CMP size:2 source:Source::Immediate destination:Source::IndBPPlusDI operand:0x4];
+	[self assert:instructions[2] operation:Operation::SUB size:2 source:Source::Immediate destination:Source::IndBX operand:0x9];
+}
+
 @end
diff --git a/Processors/Decoders/x86/x86.cpp b/Processors/Decoders/x86/x86.cpp
index 576a14487..25f05a7cd 100644
--- a/Processors/Decoders/x86/x86.cpp
+++ b/Processors/Decoders/x86/x86.cpp
@@ -585,7 +585,7 @@ std::pair<int, Instruction> Decoder::decode(const uint8_t *source, size_t length
 
 						// Sign extend if a single byte operand is feeding a two-byte instruction.
 						if(operation_size_ == 2) {
-							operand_ |= (operand_ & 0x80) ? 0xff : 0x00;
+							operand_ |= (operand_ & 0x80) ? 0xff00 : 0x0000;
 						}
 					break;
 					case 2:		operand_ = inward_data_ >> 48; inward_data_ <<= 16;	break;